1. Field of the Invention
The present invention relates to a plasma display panel and a manufacturing method thereof, and more particularly to a plasma display panel and a manufacturing method thereof that is adaptive for preventing color mixture between adjacent cells.
2. Description of the Related Art
Generally, a plasma display panel (PDP) excites a phosphor material to emit light by using an ultraviolet ray of 147 nm generated when discharging an inactive mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe, thereby displaying a picture including characters or graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides highly improved picture quality owing to a recent technical development. Especially, a three-electrode AC surface discharge PDP has an advantage in low voltage drive and long life span because wall charges are accumulated on a surface upon discharge and electrodes are protected from sputtering generated by the discharge.
Referring to FIG. 1, a discharge cell of a conventional three-electrode AC surface-discharge PDP includes a scan electrode Y and a sustain electrode Z provided on an upper substrate 10, and an address electrode X provided on a lower substrate 18. Each of the scan electrode Y and the sustain electrode Z includes a transparent electrode 12Y and 12Z, respectively, each having a metal bus electrode 13Y and 13Z, respectively, formed on one side edge of the corresponding transparent electrode. The metal bus electrode 13Y, 13Z has narrower line width than the transparent electrode 12Y, 12Z.
The transparent electrode 12Y, 12Z is formed of Indium Tin Oxide (ITO) on the upper substrate 10. The metal bus electrode 13Y, 13Z is generally formed of metal such as Chrome Cr on the transparent electrode 12Y, 12Z and it acts to reduce voltage drop caused by the transparent electrode 12Y, 12Z, resistance of which is high. An upper dielectric layer 14 and a protective film 16 is deposited on the upper substrate 10 where the scan electrode Y and the sustain electrode Z are formed in parallel. The wall charges generated upon plasma discharge are accumulated in the upper dielectric layer 14. The protective film 16 prevents the damage of the upper dielectric layer 14 caused by the sputtering generated upon plasma discharge and also increases emission efficiency of secondary electrons. The protective film 16 is generally made of Magnesium Oxide MgO.
A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18 provided with the address electrode X and a phosphorous layer 26 is formed on the surface of the barrier ribs 24 and the lower dielectric layer 22. The address electrode X is formed to cross the scan electrode Y and the sustain electrode Z. The barrier ribs 24 are formed in stripe or lattice shape to prevent the ultraviolet ray and the visible ray, which are generated by discharge, from leaking to the adjacent discharge cells. Inactive mixture gas is injected into a discharge space provided among the upper substrate 10, the lower substrate 18 and the barrier ribs 24.
The phosphorous layer 26 is made of a type of phosphor material excited by the ultraviolet ray emitted by vacuum ultraviolet ray VUV, and is divided into red phosphor, green phosphor and blue phosphor in accordance with the wavelength of the emitted light. Normally, the red phosphor is (YGd)BO3:Eu3+, the green phosphor is Zn2SiO4:Mn2+, and the blue phosphor is BaMgAl10017:Eu2+. Such red, green and blue phosphor is printed inside the PDP in screen printing method while it is in paste state.
FIGS. 2A to 2C are views representing a prior art phosphor printing method.
Referring to FIG. 2A, firstly a phosphor paste 30 is prepared by mixing the phosphor material R, G and B, resin and solvent together. Herein, the resin is high molecular Ethyl Cellulose, the solvent is a solution, which has a boiling point higher than 100° C., such as N-methyl Pyrrolidone, Ethyleneglycol, 2-Butoxy ethoxy ethanol, cellosolve and so on.
More specifically describing, the phosphor should be prepared to be in paste state in order to print the phosphor. That is, the phosphor material is mixed with the resin and the solvent in order that the phosphor can be inserted into the discharge space 39 located inside the PDP. Herein, the resin is high molecular Ethyl Cellulose, the molecular weight of which is high. If the high molecular resin is mixed with the phosphor material, the phosphor material can have a viscosity which is required for printing.
The phosphor paste 30 is spread on a mask 34 as in FIG. 2A in order to print the phosphor in the discharge space 39. The mask 34 includes a printing area 36 and a shielding area 38 as in FIG. 3. The printing area 36 is formed in mesh to allow the phosphor paste 30 to pass through to the discharge space 39. For this, the printing area 36 is located to overlap the discharge space 39. The shielding area 38 is formed to overlap the barrier ribs 24 to prevent the phosphor paste 30 from being supplied to the barrier ribs 24.
After the phosphor paste 30 is spread over the mask 34, a squeeze 32 is moved in one direction and applies a designated pressure to the phosphor paste 30, accordingly the phosphor paste 30 is passed through the printing area 36 of the mask 34 to the discharge space 39. In fact, the phosphor paste 30 that passed by the printing area 36 is printed in the discharge are 39 inside the PDP as in FIG. 2B.
However, such a prior art phosphor paste 30 is mixed with the high molecular resin, i.e., it has high viscosity, thus a lot of the phosphor paste 40 remain at the border area of the shielding area 38 and the printing area 36. In this way, the remaining phosphor paste 40 flows into the upper part of the barrier ribs 24 and the adjacent discharge cells as in FIG. 2C when the mask 34 is eliminated. Herein, the remaining phosphor paste 40 that flew into the upper part of the barrier ribs 24 and the adjacent discharge cells causes color mixture when driving PDP, thereby deteriorating the display quality.
Therefore, in the end, the phosphor paste 40 remaining at the mask 34 is eliminated by use of a cleaning tape. However, even though the phosphor paste 40 remaining at the mask 34 is removed by use of a cleaning tape, plenty of the remaining phosphor paste 40 flows into the barrier ribs 24 and the adjacent discharge cell. In addition, because the phosphor paste 30 with high viscosity is used in prior art, a lot of phosphor paste 40 remains at the mask 34, thus the cleaning tape must be used more frequently. However, if the cleaning tape is frequently used, there is a problem in that its process time and manufacturing cost increase. In addition, the phosphor paste 30 is manufactured in use of the high molecular resin. However, the phosphor including the high molecular resin has a disadvantage in a short life span according to the experiment.